Challenge: Find 500,000 Near-Earth Asteroids

A privately funded space telescope will hunt for objects on a collision course with Earth

Humankind lives in a cosmic shooting gallery. For evidence of that, we need look no further than the events of 15 February 2013. On that day, a medium-size asteroid was set to pass some 28,000 kilometers from Earth, unusually close and well within the orbits of geosynchronous satellites. Dubbed 2012 DA14, the rock was first spotted the previous year. Since then, astronomers had been eagerly anticipating the opportunity to take a closer look and measure such vitals as size, shape, and composition.

But just as they were readying their telescopes, another asteroid took them completely by surprise. In the early morning hours of the 15th, a previously unknown piece of space flotsam entered Earth’s atmosphere and streaked across the sky, breaking up over the Russian city of Chelyabinsk. Briefly exceeding the sun in brightness, the rock exploded with the equivalent of 500 kilotons of TNT.

A team of former astronauts and scientists at the B612 Foundation, a nonprofit planetary-defense group, as well as engineers at Ball Aerospace & Technologies Corp., have devised a space mission, called Sentinel, that could go a long way toward finding asteroids on collision courses before they pose a danger to Earth.